1. Field of the Invention
This invention pertains to a novel resealable pressure relief vent valve which can be used in containers which are air and fluid tight. More particularly, the present invention relates to an improved resealable pressure relief vent valve which is capable of relieving the build-up of excessive gas pressures within a closed container such as an energy cell. When said pressure is relieved, the vent closes providing the cell with its air and fluid-tight configuration.
The valves of the present invention have particular application in containers such as electrical batteries or cells which are inexpensive yet which must be provided with a reliable valve which has good endurance to function the entire life of the battery or cell. Therefore, the valves of the present invention are particularly characterized by their relative inexpensive cost of manufacture, simplicity of design and reliability.
The term battery is generally used to describe a single unit comprising one or more cells which supply electrical energy. The electric current is produced directly by chemical reaction which occurs within the battery. The terms battery and cells will be used hereinafter interchangeably.
The resealable vent devices of the present invention are useful in sealed cells in contrast to vented cells. A sealed cell, in its normal operation, does not require the venting of gas to the atmosphere. However, in a vented cell, venting is part of the normal operating behavior of the cell. Although sealed cells contain a vent mechanism, they are still referred to as "sealed" cells because the vent operates only as a safety measure when, as a result of a malfunction or an abuse of the cell, the cell obtains an abnormally high internal pressure.
In a sealed cell, the safety vent mechanism is designed to open if the pressure exceeds a certain limit. After the vent releases the excess pressure to the atmosphere, it automatically closes, sealing the cell. For this reason, it is called a resealable safety vent. The vent is incorporated in the cell or battery to protect the cell by opening to relieve damaging high pressure, and resealing the cell so that it does not remain open to the atmosphere and cause the electrolite to dry out.
The vent devices of the present invention have a resealing capability. Resealable safety vents are generally preferred to non-resealable vents in sealed cells for various reasons. Resealable vents can be tested prior to assembly into a cell casement to help assure reliable operation. The resealing feature allows the cell to operate after the excess pressure has been relieved. Cells containing a non-resealable vent will not function properly after venting because the electrolite within the cell will dry out as the vent remains open.
While the resealable safety vents of the present invention may be utilized on most sealed cells which potentially could experience increases in internal pressure, nickel-cadmium cells are discussed in greatest detail herein. Such cells are merely illustrative and examples of other cells that may be used include carbon-zinc dry cells and "alkaline" cells. The operating pressures for each of these cells and other cells vary from those of nickel-cadmium cells and the resealable vent devices of the present invention may be suitably adapted to be used at pressures other than those in nickel-cadmium cells.
As used herein, the term vent pressure means that internal pressure that will cause the vent in the cell to open.
2. Description of the Prior Art
Resealable pressure relief vent valves of various designs have been used in the past for releasing high internal gas pressures from the inside of a sealed electrical cell or battery such as a nickel-cadmium cell. These valves generally utilize a valve member such as a flat rubber gasket which is situated in a sealing position over a vent orifice by means of a resilient member such as a helical spring. The resilient member or spring is set to yield at a certain predetermined internal gas pressure which momentarily breaks the seal and allows the gas to escape through the vent orifice. Examples of such pressure relief vent valves are described in U.S. Pat. No. 3,664,878 in the name of H. K. Amthor; U.S. Pat. No. 3,484,301 in the name of E. E. Gray; and U.S. Pat. No. 3,293,091 in the name of J. L. S. Daley. All of these patents disclose devices whose configuration require critical tolerances to enable the valve system to function properly. As brought out in U.S. Pat. No. 3,644,878, a major problem encountered with such valves is that they are bulky and difficult to incorporate into the cell assembly.
Conventional devices utilizing metal springs are extremely costly and require very close tolerances to attain the desired force exerted by the springs. Moreover, the labor costs in fixing the springs in the cell is substantial. The vent device of the present invention has none of these disadvantages attributed to spring-type vents.
Another advantage of the vent device of the present invention over the conventional spring vent devices is that it requires substantially less space, particularly for its height, in the cell. The reduction in height is attributed to the elimination of the spring component in the vent device of the present invention. By reducing the space required for the vent section, a battery containing the vent device of the present invention can contain more energy-producing materials yielding a battery having an increase in energy density over a comparable cell utilizing conventional vent devices.
The resealable vent device of the present invention overcomes these and other problems and provides numerous additional advantages over known resealable pressure relief valves.